An yttrium aluminum garnet (hereinafter, YAG) is an oxide generally shown by a composition formula of Y3Al5O12, and is a material used as a raw material of a laser oscillation device, a decoration goods, a high temperature material, a material for various detective devices, an alternative material for sapphire, a transparent ceramic material, and so forth. Materials having part or all of yttrium or aluminum therein replaced with other elements as well as those containing a dope element have been reported; and thus, these are very useful industrially. However, emission characteristic such as fluorescence characteristics and other characteristics such as strength, heat resistance, corrosion resistance, and transparency, change with molar ratios of the constituent elements of YAG; and thus, a YAG microparticle having the molar ratios thereof controlled is required.
As to the producing method of the YAG microparticle, several methods have been developed which include: a conventional method, as shown in Patent Document 1, in which yttrium oxide and aluminum oxide, optionally together with a sintering adjuvant, are crushed and mixed by a ball mill or the like, and then, after the mixture is subjected to a solid phase reaction at high temperature for a prescribed time, it is crushed again by a ball mill or the like to pulverize; and a conventional method, as shown in Patent Document 2 and Patent Document 3, in which an acidic solution which contains an yttrium ion and an aluminum ion is neutralized by a basic substance such as sodium hydroxide to co-precipitate an yttrium compound and an aluminum compound, and then the obtained co-precipitates are subjected to heat treatment to synthesize YAG. However, in these conventional methods, not only producing of the YAG microparticle, especially those having the size of 1 μm or less, has been extremely difficult, but also it has been very difficult to make the molar ratios of the constituent elements in the YAG microparticle homogeneous. In the conventional technology described in Patent Document 2, as it is described therein, besides a problem that there occurs contamination of impurities derived from a ball mill and the like when pulverization is carried out by using a pulverization method which mainly uses a ball mill that uses a ball or the like as a crushing medium, there have been a problem such as the one in which intended various characteristics including fluorescence characteristics of the obtained YAG microparticle cannot be expressed readily due to a physical impact given to the crystal thereof.
Applicant of the present invention provided a method for producing a ceramic microparticle as shown in Patent Document 4; however, in it, specific methods for producing neither a YAG precursor microparticle nor a YAG microparticle, with the molar ratios of the constituent elements in these microparticles being controlled, have been disclosed. Therefore, methods of producing a YAG precursor microparticle and a YAG microparticle, with the molar ratios of the constituent elements in these microparticles being controlled, have been eagerly wanted. In addition, including the YAG precursor microparticle and the YAG microparticle, methods for producing a precursor of a microparticle having a garnet structure and a microparticle having a garnet structure, with the molar ratios of the constituent elements in these microparticles being controlled, have been eagerly wanted.